Sorry for the massive noob question here. I'm getting started from Fusion, I have been using After Effects for years.

What I'm really trying to do is so simple yet I'm going round in circles trying to do it. I'm trying to make a luminance matte, by clipping the black and white values of a plate. In After effects I'd use a Levels or Curves effect. In Nuke I believe you can use the Keyer. Here I can't find a way of doing it! Even the Color Curves tool which looks familiar to the AE curves tool doesn't behave at all like I was expecting (Adjusting the In and Out points appears not to do anything...) and there's no simple tool to simply adjust the Black/White point.

Sorry again for the noob question, I don't know where else to look. Any help?

in the brightness/contrast node you have a slider for the low and high value, maybe you chould also check the clip black/white checkboxes, because if you work in float you can get values below 0 and above 1

in the colorcorrect on the levels tab, the sliders for the histogram do for me the same as expected. either they crush the blacks or the clip the white values

you can also use the luminance keyer

or use the bitmap mask set to luminace and adjust the low and high value there

I have tried those methods and they seem to work now. It appears my problem lies with the source footage:For instance – the low/high point on the Brightness/Contrast node doesn't do anything on a 32bit float EXR file, however works fine on a 16bit EXR. Similarly, weird shenanigans with colour curves on 32bit footage.

Are some nodes not 32bit compatible, and is it better to work in 16bit?

I may be mistaken, but I think very few image tools are half float. I can't think of any off the top of my head, actually. Last time I checked, they all process full float, promoting a half input to float, processing, then converting back to half.